Currently, there has been increasing demand for greater capacity and reduced sizes of magnetic disk devices which are used as external recording devices for information processors, such as computers. This has forced designers to attempt to increase the recording density in magnetic recording devices. Perpendicular recording systems, which make it easier to increase the recording density, have therefore become the most common systems, rather than the conventional longitudinal recording systems.
Perpendicular magnetic recording systems comprise at least a perpendicular recording medium having perpendicular anisotropy at the film surface, and a magnetic head for perpendicular recording which has the function of effectively applying a perpendicular magnetic field to the medium. The magnetic head for perpendicular recording comprises at least a coil conductor and a magnetic circuit which is interlinked therewith, and the magnetic circuit comprises a sub-pole and a main pole. A recording current, in which the polarity is set in accordance with electrical signals, flows to the coil conductor, and causes a recording field having a corresponding current polarity to be generated by the main pole. The main pole faces the recording medium and magnetizes the recording layer directly below. Changes in the polarity of the recording field are recorded as changes in the direction of magnetization of the recording medium. A soft magnetic underlayer is disposed below the recording layer which forms part of the perpendicular recording medium, and this has the function of returning the magnetic flux acting on the recording layer to the sub-pole. In order to improve the efficiency of this function, the sub-pole is designed with a greater surface area on the surface facing the recording medium than the main pole. This design allows magnetic information to be recorded onto the perpendicular recording medium as changes occur in the direction of magnetization.
In perpendicular recording, it is increasingly desired to narrow the magnetic transition width (which determines the recording density limit) which is present between adjacent regions of reverse magnetization in order to record high-density magnetic information (which is present in regions of different magnetization).
It is widely known that the magnetization transition width is affected by the magnetic field gradient of the recording head, and Japanese Unexamined Patent Appl. Pub. No. 2004-310968 discloses a magnetic head for perpendicular recording which has a soft magnetic film on the side surface in the track width direction of the main pole as a method for increasing the magnetic field gradient. Furthermore, Japanese Unexamined Patent Appl. Pub. No. 2005-18851 discloses a magnetic head for perpendicular recording in which the magnetic field gradient is made steeper by providing a soft magnetic film on the trailing side of the main pole. Furthermore, Japanese Unexamined Patent Appl. Pub. No. 2005-190518 and Japanese Unexamined Patent Appl. Pub. No. 2007-35082 propose a structure in which a magnetic shield film is provided that surrounds the periphery of the main pole. Japanese Unexamined Patent Appl. Pub. No. 2007-294059 discloses a structure in which the distance between the main pole and a side shield (the side gap length) is varied in the depth direction from the air bearing surface. Furthermore, Japanese Unexamined Patent Appl. Pub. No. 2004-127480 discloses a structure in which the shape of the side shield in the depth direction from the air bearing surface becomes larger moving away from the main pole. Inside the magnetic shield, the side of the main pole is positioned in order to prevent leakage of the magnetic field to adjacent tracks, and the upper side (trailing side) is positioned in order to increase the magnetic field gradient. In addition, Japanese Unexamined Patent Appl. Pub. No. 2009-4068 discloses a structure in which the trailing side of the main pole becomes thicker in the depth direction from the air bearing surface, and a thick nonmagnetic film is placed on the trailing side where the main pole has been thickened.
According to the prior art presented above, the side of the main pole can prevent leakage of the magnetic field to adjacent tracks when a soft magnetic film is provided around the main pole, and the upper side (trailing side) can increase the magnetic field gradient, and therefore narrowed track recording may be achieved. However, among other issues, there are problems in that the magnetic field intensity is reduced by a combination of the thickness of the soft magnetic film and the saturation magnetic flux density, and there are also problems in that data is recorded to adjacent tracks by the shield film effectively overwriting already recorded information, and these problems are an obstacle to narrower track recording.
Therefore, it would be beneficial to have a magnetic head which can overcome these deficiencies while still providing an increase to the intensity of the magnetic field and suppresses writing to adjacent tracks.